A substrate processing apparatus is used in the process of manufacturing semiconductor devices, liquid crystal panels, or the like. The substrate processing apparatus is configured to supply a treatment liquid to a surface of a substrate, such as a wafer or a liquid crystal substrate, to thereby treat the surface. Among such substrate processing apparatuses are spin processors. The spin processor is configured to supply a treatment liquid to substantially the center of a surface of a horizontally rotating substrate so that the treatment liquid spreads over the surface by the centrifugal force of the rotation. Further, there have been developed such spin processors that collect used treatment liquid to recycle it.
For example, to remove a resist from a surface of a substrate with a substrate processing apparatus as described above, SPM treatment is applied using a SPM (a mixture of sulfuric acid solution and hydrogen peroxide water) as a treatment liquid. In the single wafer processing of a substrate with SPM treatment, SPM is supplied to the substrate by several approaches such as mixing a sulfuric acid solution and hydrogen peroxide water in advance and then the mixture is supplied or mixing them on the substrate. After the removal of the resist, the substrate is washed and dried, or treated by a different treatment liquid after having been washed, then washed again and dried. After that, the substrate is passed to the next process.
There is a case where the SPM treatment using SPM only is insufficient. For example, when ion implantation is performed on a surface of a substrate, the surface of a resist film is cured (altered) thereafter. It is difficult to remove the cured resist by the SPM treatment, and some resist remains on the substrate. Therefore, to improve the treatment performance, high-temperature SPM (e.g., 160° C.) is sometimes used to treat the substrate.
However, the life of hydrogen peroxide water is reduced as its temperature rises. Accordingly, when mixed with a sulfuric acid solution and has a high temperature, the hydrogen peroxide water has been being decomposed before arriving at the substrate, resulting in insufficient improvement in the treatment performance. If a large amount of hydrogen peroxide water is mixed with a sulfuric acid solution to keep the water left, the sulfuric acid solution is attenuated. This makes it difficult to recycle the treatment liquid, thereby increasing the total usage of the treatment liquid. Besides, when hot sulfuric acid solution and hydrogen peroxide water are mixed together, bumping of the hydrogen peroxide water, i.e., bumping (violent boiling) of H2O of H2O2, occurs as they are not fully mixed. As a result, the hydrogen peroxide water evaporates. More specifically, when high-temperature sulfuric acid solution (160° C.) is brought in contact with hydrogen peroxide water, H2O, i.e., a component of the hydrogen peroxide water, boils rapidly by the temperature of the solution. Because of this phenomenon, the hydrogen peroxide water evaporates before mixed with the sulfuric acid solution, and therefore, oxidizing substances, such as peroxymonosulfuric acid and peroxydisulfuric acid, which contribute to resist stripping are not generated. This may result in insufficient improvement in the treatment performance. From these factors, improvement in the treatment performance and reduction in the usage of treatment liquid are desired.